Method of phenol tar desalting

ABSTRACT

A method for reduction of salt content in phenol tars with no additional solvent which washes the tars with water alone in a countercurrent flow extractor and substantially reduces the level of salt in the tar.

This is a continuation of application Ser. No. 08/531,352 filed on Sep.20, 1995.

This invention relates generally to the process for manufacture ofphenol from cumene. In this process, cumene is first oxidized to acumene hydroperoxide intermediate which is then decomposed with an acidcatalyst in a second step to form the crude mixture of phenol, acetoneand by-products. Prior to distillation and products recovery, it isnecessary to remove the catalyst acid via a neutralization process usingbase. The inorganic salts that are formed here and partially exit theprocess with the tars that are formed must be effectively removed toprevent fouling of downstream equipment and contamination of the phenoltar stream which is incinerated.

As environmental restrictions become more stringent, it is critical tolower the volume of unusable wastes generated by the process. One of themore promising avenues in minimize wastes is to recover more usefulproducts from the tar streams. However, the presence of salts in thetars interferes with these recovery processes by causing equipmentfouling and corrosion. As the residual tar volume decreases the saltconcentration increases, thus, leading to corrosion problems in theincineration system. Thus, an efficient tar recovery and dispositionsystem requires an innovative efficient approach to lessen the saltlevels in these tars to facilitate product recovery from these tarstreams and lessen the level of corrosion and fouling in disposalequipment

The phenol tar stream is a complex material consisting of manycomponents including phenol, acetophenone (AP),α,α-dimethylbenzylalcohol (DMBA), dimers of α-methylstyrene (DMS)o,p-cumylphenol (PCP), unidentified components, and small amount ofsalts (mainly Na₂ SO₄) and a methylstyrene (AMS). The exact phenol tarcomposition is dependent on the specific phenol production technologyand can vary over a wide range.

    ______________________________________                                        Component     Weight percent                                                  ______________________________________                                        AP            5-30                                                            PCP           10-50                                                           Phenol        5-40                                                            DMS           3-35                                                            DMBA          1-15                                                            Residue       1-65                                                            Salts         0-2                                                             AMS           less than 0.1                                                   ______________________________________                                    

Because of the presence of salts and the variation in composition,phenol tar has not found uses of substantial commercial value and isprimarily used as fuel oil or incinerated as waste of no value. However,even when incinerated, the presence of both salts and phenol in the tarcauses unacceptable air pollution by the phenolic compounds andparticulates produced in incineration and corrosion and scale build upin the burners because of the salt content.

To date phenol tar processing has been aimed at phenol recovery sincephenol is present in the tar in a relatively large quantity and hassubstantial value. In these processes, removal of salt is either notattempted or requires a completely separate process as set forth in U.S.Pat. No. 5,283,376.

One method disclosed for phenol tar desalting processed the tar at atemperature of from 50°-60° C. with sulfuric acid mixed with the tar inan amount to provide 10% acid by weight based on the total quantity ofphenol tar. The resultant reaction mass was washed with water, allowedto settle and the phenol tar was separated from the salt solution bydecanting. Unfortunately this method substantially increases the levelof waste water generated causing a greater deleterious impact on theenvironment.

Another method uses ammonia to extract phenol from the phenol tar. A 2to 5% by weight ammonia solution in water at ambient temperature ismixed with phenol tar at a weight ratio of from 1 to 1.5 to 1 to 4,allowed to settle and then separated into organic and water phases. Thelevel of salt removal depends on the effectiveness of the extractingagent. Other shortcomings of this process are:

1. Large volume and cost of the extracting agent increases the cost ofthe process and requires large volume equipment to accommodate the highvolume of extracting agent. 2. Phenol tar must be cooled to about 25° C.before entering the extraction process to avoid excessive loss ofammonia through evaporation. This increases tar viscosity making the tarmore difficult to handle.

As can be seen, each of the prior art processes for tar desalting havethe common disadvantage of employing a water borne extracting agentwhich requires periodic regeneration. Regeneration increases costs andrequires additional investment in equipment for regeneration of theextracting agent.

In order to overcome these disadvantages, the present invention:

provides an equivalent level of desalting efficiency with a substantialreduction in extracting agent usage

expands the temperature range of the desalting process

desalts the phenol tar with water alone as extractant, without theaddition of any chemicals

does not form emulsions which then must be broken

The method of the present invention comprises contacting at atemperature of from about 10° C. to about 90° C. phenol tar containingsalt with water at a feed ratio by weight of phenol tar to water of atleast 0.3 to 1 in a multi-stage counter current flow extractor unitwhereby the tar and water are admixed. The salt is removed in the watereffluent Because no additives are required in order to extract the saltsfrom the tar, the water and tar phases rapidly separate after admixtureefficiently removing substantially all of the salts from the tar. Sinceneither water in organic or organic in water stable emulsions areformed, no additives are needed to break the emulsions as necessary inthe processes of the prior art. The efficiency of a counter currentwater wash was not heretofore recognized by skilled artisans because theprior art processes failed to provide the high degree of phaseseparation of the tar and water streams afforded by the counterflow ofthe present process.

For maximum extraction efficiency the water passes through theextraction vessel only once and then is disposed of in an ecologicallyeffective manner. In water shortage areas, the water can be recirculatedto the countercurrent extractor up to as many as 5 times, preferably 3times and more preferably 2 times and still maintain acceptableextraction efficiency. It is more economic to recirculate the water thanto raise the phenol tar to water feed ratio above 0.3 to 1. However, intimes of extreme water shortage the extraction process will reduce saltlevels somewhat when the ratio is as high as 0.5.

With respect to the temperature of the extraction process it is operatedfrom about 10° C. to about 90° C., preferably from about 15° C. to about80° C. and more preferably from about 20° C. to about 70° C. In thepresent process, the salt range in the phenol tar is reduced from0.11-1.10% by about 20% by weight, preferably 90% and more preferably99%. The key to the extraction process is the intimate admixture of thephenol tar and the water followed by efficient phase separation. Noextra solvents are employed to dilute the phenol tar to make it lessviscous in order to facilitate intimate admixture and then efficientphase separation.

Surprisingly the direct contact of undiluted phenol tar with water alonein the present process gives superior extraction performance. Admixtureof phenol tar alone with water alone is usually sufficient as a resultof the turbulence from the countercurrent flows in the reactor. Intimateadmixture may be enhanced by installing in the extractor any of thestate of the art mixing devices such as strategically located baffleswhich act as static mixers, paddles, anchor stirrers reciprocatingtrays, pulsing column extractor or any like devices of the prior artwhich increase turbulence in the extractor. In a multi-stage pulsingcolumn, a reciprocating pump "pulses" the entire contents of the columnat frequent intervals, so that a rapid reciprocating motion ofrelatively small amplitude is super-imposed on the usual flow of theliquid phases. The multi-stage tower may contain ordinary packing ofspecial sieve plates. In a packed tower the pulsation disperses theliquids and eliminates channeling, and the contact between the phases isgreatly improved. In sieve-plate pulse towers the holes are smaller thanin nonpulsing towers, ranging from 1.5 to 3 mm in diameter, with a totalopen area in each plate of 6 to 23 percent of the cross-sectional areaof the tower. Such towers are used almost entirely for processing highlycorrosive reactive liquids. No downcomers are used. Ideally thepulsation causes light liquid to be dispersed into the heavy phase onthe upward stroke and the heavy phase to jet into the light phase on thedownward stroke. Under these conditions the stage efficiency may reach70 percent. This is possible, however, only when the volumes of the twophases are nearly the same and where there is almost no volume changeduring extraction. In the more usual case the successive dispersions areless effective, and there is backmixing of one phase in one direction.The plate efficiency then drops to about 30 percent. Nevertheless, inboth packed and sieve-plate pulse columns the height required for agiven number of theoretical contacts is often less than one-third thatrequired in an unpulsed column.

To provide intensive mass transfer in a pulsing extractor, liquids incontact are in oscillating (push-pull) motion of defined amplitude andfrequency. Thus, vibration motion frequently is transformed into othertypes of motion in the contact units (e.g. into rotating movement). Thisleads to more even distribution or dispersion of one phase in to theother and increases the contact surface between the phases. Moving incontinuous phase, dispersed particles combine or coalesce forming largerdrops which split and return to the contact units. So, pulsationprovides multiple surface interations and increases the surface area byreduction of average drop dimension. All this increases the masstransfer index.

In the hydrodynamic mode of a pulsing column equipped with contact units(trays), operation is determined by the physical and chemical propertiesof the phases in contact (surface tension, viscosity, difference indensities, etc.) and pulsation intensity. Pulsation intensity Jordinarily is characterized as twice the amplitude multiplied by thepulsation frequency.

To perform salt extraction from phenol tar using water, a countercurrentcolumn-type multi-stage pulsing extractor is preferable. Extractant(water) feeds into the bottom part of the column and fills it as acontinuous phase. The extract output exits from the top of the column.Phenol tar (heavy phase) feeds into the top of column, goes through thecolumn in a direction opposite to the flow of extract and is dispersedon the trays. Desalted tar collects in the bottom of the column andexits the reactor from the bottom. Phase pulsation is provided by anexternal pneumatic pulsator.

There are several hydrodynamic modes of the pulsing column operationdependent on pulsation intensity:

1. Insufficient pulsation intensity. One can observe column "choke",i.e. one of the phases locks into the other one, stopping it to fromgoing through the column. There is no mass transfer in this mode.

2. Pulsation intensity is increased. Hydrodynamic of this modecorresponds to a discrete mixer--sedimentator mode. During theoscillation phase when the liquid goes down, phenol tar (heavy phase),which forms a layer on the tray, squeezes through the tray holes aslarge globules which drop onto next lower tray, where they coalesce. Inthe next oscillation phase, when the liquid goes up, the light phase(water) runs through the tar layer and phase inversion occurs. In everypulsation cycle, the heavy phase shifts down one tray. Thismixing-sedimentating mode is not very effective because of the shortcontact time and small phase contact surface.

3. A further increase of pulsation intensity provides a split of dropsand decreases the rate of their shifting from tray to tray. This modeprovides a highly effective mass transfer. Ordinarily, industrialextractors are operated in this manner. Such a dispersion system can becharacterized by an even distribution of similar size drops of the heavyphase which fill all of the between-tray volume. The contact surface inthis case is several times more than it is in the second mode, and masstransfer index is of the highest value.

4. A higher pulsation intensity leads to unstable regime which can becharacterized by a more tight drop pack and local coalescence (formationof unstable emulsion aggregates, leading to local "chokes").

5. A further rise of pulsation intensity leads to total "choking" of theextraction column.

The pulsing operation mode provides a well-dispersed heavy phase movingthrough the continuous light phase without emulsion formation andmechanical capture of either phase by the other for systems such asphenol tar--water, having a small density difference of about 0.05g/cm³). It is preferable to maintain phenol tar flow through theextractor to provide a residence time of the tar of at least 2, morepreferable at least 5 and most preferable at least 10.

The actual equilibrium stages of phase contact are an indication ofintimate admixture achieved. In the practice of the present invention,the actual equilibrium stages of phase contact are usually in the rangeof from about 1 to about 10 , preferably from about 2 to 8 , morepreferably from about 3 to about 6 and most preferably from about 3 toabout 4.

Whereas the prior art has focused on the need for chemicals to enhanceextraction efficiency, the inventors hereof have determined that wateralone is most effective with adequate admixture. Adequate admixtureresults when the pulsation intensity provides a splitting of the tarinto droplets and decreases the rate of shifting of the tar dropletsfrom tray to tray. This level of pulsation intensity is accomplished bygradually increasing the pulsation intensity until tar droplets arevisible through lighted observation ports in the reactor. When adjustedto this level of pulsation intensity quite readily by the skilledartisan an even distribution of tar droplets of substantially the samesize is formed and these droplets of tar dispersed in watersubstantially fill the entire volume between the trays, maximize thecontact surface between the continuous water phase and the discontinuoustar phase and give a mass transfer index of the highest value.

Thus, the advantages of the present process are;

1. Usage of water alone as an extracting agent gives minimal reagentcost.

2. No dilution of phenol tar with solvent reduces environmental impact.

3. No additional solvents or chemicals needed for intimate admixture orefficient phase separation.

4. Broad temperature range gives highly flexible operation.

5. High degree of salt removal (over 95%).

6. Tar/water equilibrium is achieved almost immediately.

The advantages of the process suggested are confirmed by the followingexamples:

EXAMPLE 1.

A phenol tar stream having a composition wt. % as follows: salts 0.139,phenol 17.2, AP 19.2,, DMBA 11.8, DMS 10.6, AMS 0.08, CP 15.1 andunknowns 3.82, is processed by counter-current liquid extraction withwater at 85° C. in a multi-stage pulsing column extractor.

The feed ratio of phenol tar to extracting agent (water) is 1:0.5. Theextractor provides 6 theoretical equilibrium stages of phase contact.The water and tar streams rapidly separate after leaving the pulsingcolumn extractor into two phases which are separated by decanting.

As a result of this extraction process a sufficient quantity of thesalts is removed from the phenol tar so that the salt content remainingin the tar is 0.001% which corresponds to degree of salt removal equalto 99.2%.

EXAMPLE 2.

Phenol tar (same composition as in Example 1) is processed by water inthe pulsing column extractor providing 3 theoretical equilibrium stagesof phase contact at 25° C. and feed ratio of tar to water is 1:1.5. Theremaining salt content at extractor outlet was 0.003%, degree of saltremoval was 97.8%.

EXAMPLE 3.

Phenol tar stream of following composition, % by weight. salt 0.087,phenol 15.72, AP 17.52, DMBA 6.68, DMS 7.08, AMS 0.43, PCP 11.37,unknown components to 100%, is fed to the extractor as in Example 1 withwater at a pulsation intensity J=44 mm/sec., a feed ratio of 1/1,temperature of 50° C. The extractor provides 3 theoretical stages ofphase contact Salt remaining in the phenol tar after exiting theextractor is 0.0015 weight % which corresponds to a degree of extractionof 98.3% by weight.

EXAMPLE 4.

Phenol tar of the same composition as in Example 3 is fed into theextractor of Example 1, with water at a temperature of 50° C., pulsationintensity of 15 mm/sec., feed ratio of water/phenol tar of 0.75/1. TheExtractor provides 1 theoretical stage of phase contact Salt remainderin phenol tar after extractor is 0.053 weight % which corresponds to adegree of extraction of 36% by weight.

It should be understood that the examples are given for the purpose ofillustration and do not limit the invention.

We claim:
 1. A process for reducing the level of salt resulting fromneutralization of catalyst acid in a phenol tar from aphenol-from-cumene process, which comprises; admixing in a multi-stagecounter current flow extractor the phenol tar, which comprises salt, ata temperature of from about 10° C. to about 90° C. with an extractionliquid consisting essentially of water, in a tar to extraction liquidfeed ratio of at least 0.3/1, wherein the tar and extraction liquid donot form a stable emulsion and the level of salt is reduced by at least20 percent by weight.
 2. The process of claim 1 wherein the extractorhas baffles which act as a static mixer to increase the intensity ofadmixture of the counter current flow.
 3. The process of claim 1 whereinthe extractor contains agitation means additionally to counter currentflow.
 4. The process of claim 3 wherein the agitation means is arotating anchor stirred.
 5. The process of claim 3 wherein the agitationmeans is rotating paddles.
 6. The process of claim 3 wherein theagitation means is reciprocating trays.
 7. The process of claim 3wherein the agitation means is a pulsing column extractor.
 8. Theprocess of claim 1 wherein the residence time of the tar in theextractor is at least ten minutes.
 9. The process of claim 7 wherein theextractor provides at least one theoretical equilibrium stage of phasecontact.
 10. The process of claim 1 wherein the water is recirculated tothe extractor at least once.
 11. The process of claim 1 wherein thewater is not recirculated to the extractor.
 12. The process of claim 1wherein the extractor is a multi-stage pulsing column extractor.
 13. Theprocess of claim 12 wherein the phenol tar containing salt and the wateroscillates at an amplitude is at least 3 millimeters and at a frequencyof at least 0.5 Herz.
 14. The process of claim 1 wherein the extractoris a packed column.